Ever since 1934, when Mary Poppins descended from the skies over London into Cherry Tree Lane in the beloved book by P. L. Travers, the world has adored the enchanting adventures and peculiar wisdom of this magical nanny. For more than eight decades, Travers's staunch but charming heroine has been beloved in the pages of eight popular books-and in media-from movies to stage, and music to television, all around the world. Now Mary Poppins has come...